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Linton Park East Detention Dam Upgrade

Te Whakahoutanga o te Pāpuni i te Papa Rēhia o Linton

Construction of a new detention dam at Linton Park East was completed in November 2024.

The dam will help control the natural flow of water during heavy rain and replaces a previous dam at the Old Taupo Road end of Linton Park East.

The original dam was built in 1998 to protect properties downstream from flooding and was built to control water flow rather than to store water for future use.

Storm water upgrades

Rotorua Lakes Council has committed to long-term infrastructure investment to enable growth, to mitigate existing stormwater issues and to prepare for the effects of climate change. Some of the work encompasses upgrades to stormwater assets, including the Linton Park East dam.

Council carried out investigations into its stormwater network, including The Linton Park East dam, to better understand what improvements could be made. The investigations highlighted the old dam did not meet modern safety requirements and engineering best practice and was no longer fit for purpose.

Illustration showing a stream, trees a path and the Linton Park dam

The original dam was built in 1998 and there have been significant advances in dam engineering and safety practices since then. A dam safety assessment highlighted several areas that needed improvement:

  • Dam embankment, and foundation strength and resilient stability required reinforcement;
  • Dam embankment seepage controls required improvement could be improved;
  • Seepage control along the culvert required improvement to protect its stability;
  • Spillway capacity required improvement to allow for better controlled discharge;
  • Freeboard (factor of safety) needed to be provided;
  • The robustness of auxiliary spillway required enhancement;
  • The overall system performance monitoring instrumentation required upgrading; and
  • Introduction of new dam safety management systems.

Council needed to carry out the improvements to protect people, property, and the environment downstream from the effects of stormwater during severe weather events. Council completed the upgrade under the emergency works provisions of the Resource Management Act (Section 330).

  • Bring the dam up to modern safety standards and accepted current industry practise;
  • Ensure the upgraded dam continued to manage stormwater flows downstream in a sustainable way;
  • No increase of flooding risk to upstream properties;
  • Provide as much flood mitigation as possible within the scope of the works to support new housing options;

The original dam had a High Potential Impact classification (PIC). A high classification meant the dam had significant safety issues in the case of failure. This also set the standards for design and ongoing management to keep the risk of dam failure to an acceptably low level. These standards are very high and include being able to safely withstand up to a 10,000-year flood event.

To meet safety standards, the dam needed to be raised and extended within the reserve. The spillway also needed to be replaced and constructed out of concrete to ensure safe operation.

The new dam now extends past the carpark on Pedlar Street, on the Mount View Road edge of the reserve.

The overall height of the dam has been raised by up to 2.6 metres. It is important to note the new dam was designed to manage stormwater during a 100-year storm event and safely manage flows beyond this. Water will only be ponded in the reserve in large events and will not fill higher than the ground level of surrounding properties.

The new dam outlet will also include a stoplog system to control flow out of the dam.

This stoplog system will enable the flood detention function of the dam to be maximised for present day rainfall.

A diagram showing the cross section of bund height at Pedlar Street carpark area

Cross section diagram of bund height at Pedlar Street carpark area.

Retrospective resource consent

As the original dam was unsafe it was rebuilt under the emergency provisions of the Resource Management Act 1991.

When operating under the emergency provisions, Council still had a duty to avoid, remedy or mitigate adverse effects.

Consequently, erosion and sediment controls were adopted, and Bay of Plenty Regional Council compliance officers regularly attended the site.

Baseline ecology studies were undertaken prior to the works starting.

During construction, vegetation was cleared to allow for the larger dam footprint. Ecologists were on site during these works to relocate any lizards or fish and bat monitoring was undertaken.

Mana whenua blessed the site prior to work beginning and have been providing input throughout the construction and preparation of resource consent documents for any ongoing effects.

Now that the construction work has been completed, Council needs to apply for resource consent for any ongoing effects of the dam with the two key areas being ecological (from the removal of vegetation) and flood risk management (ensuring that the downstream flood benefits don’t increase flooding elsewhere).

An ecological restoration plan will be developed as a condition of resource consent with planting proposed within Linton Park East.

To enable the safe operation of the new dam, the Building (Dam Safety) Regulations 2022 require a comprehensive dam safety review every five years.

The resource consent conditions propose that this will include a review of whether there have been any changes to rainfall and stormwater predictions that would change the upstream or downstream flooding extent and therefore whether any further remedial actions are required.

Other opportunities for the reserve

While the replacement of the dam was necessary to protect life, property, and our environment, it also presents an opportunity to do some enhancements on the reserve for recreational, environmental, and better place making amenity.

Council is assessing what potential enhancements are possible and what the timeline would be for any improvements. No decisions have been made at this point, but we are looking at:

  • If existing drainage of the sports fields closer to Edmund Road can be improved;
  • Enhancements to some wetlands and riparian vegetation within the reserve, to meet the ecological conditions of the retrospective Resource Consent;
  • The existing playground at Deborah Place is up for renewal – there is potential for this to be better integrated into the reserve and include some nature play space, which will be driven by feedback from community engagement;
  • Potential to create more connections to the surrounding neighbourhood and existing shared path that follows the Mangakakahi Stream.

Mangakakahi Stream improvement and protection works

Rotorua Lakes Council and Toi Moana Bay of Plenty Regional Council are working together on a programme of works to improve and protect the Mangakakahi Stream between Linton Park and Sunset Road.

The improvement and protection work will include stream bank stabilisation and removal of exotic/pest plants.

To maximise these efforts, a planting programme is planned for the stream banks. Establishing appropriate plants on the banks will enhance the natural environment, limit regrowth of exotic/pest plants and help to reduce the ongoing maintenance costs.

Lower Utuhina Catchment, Mangakakahi Stream Works Factsheet – (PDF, 2.5MB)

FAQs
Pātai Putuputu

No. It is important to note that the dam is designed to hold stormwater during a 100-year weather event. However, due to the reserve being in a low-lying area, and the height of the dam, the water would not fill higher than the ground level of surrounding properties.

Council is aware of nearby areas that experience flooding during significant weather events. This work is part of a wider range of works planned over the next few years to mitigate existing flooding issues and provide capacity for additional growth.

Upgrading the dam to ensure that it complies with the current regulations means that any risk of it failing will be mitigated. The new dam will provide better protection to the downstream industrial areas.

A 1/100-year flood will occur on average once every 100 years. In the case of a 100-year event, the probability of a storm this size occurring in any one year is 1%.

This means it is possible to have multiple “100-year floods” occurring within a 100-year period because, even if a 100-year flood event was recorded this year, the probability of another event of that size being recorded in the following year (or any other subsequent year) is still 1%

Lower Utuhina Catchment, Mangakakahi Stream Works Factsheet – (PDF, 2.5MB)

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